1. Field of the Invention
Embodiments of the invention relate to a stereoscopic image display and a method for compensating for a crosstalk of the stereoscopic image display capable of improving picture quality.
2. Discussion of the Related Art
With the advancement of various image processing techniques, stereoscopic image displays capable of implementing a three-dimensional stereoscopic image (hereinafter referred to as ‘3D image’) have been recently developed.
The stereoscopic image displays implement the 3D image using a stereoscopic technique or an autostereoscopic technique.
The stereoscopic technique, which uses a parallax image between left and right eyes of a user with a high stereoscopic effect, includes a glasses type method and a non-glasses type method, both of which have been put to practical use. In the non-glasses type method, an optical plate such as a parallax barrier for separating an optical axis of the parallax image between the left and right eyes is generally installed in front of or behind a display screen. In the glasses type method, left and right eye images each having a different polarization direction are displayed on a display panel, and a stereoscopic image is implemented using polarized glasses or liquid crystal (LC) shutter glasses.
The glasses type method is roughly classified into a first polarizing filter method using a patterned retarder film and polarized glasses, a second polarizing filter method using a switching liquid crystal layer and polarized glasses, and an LC shutter glasses method. In the first and second polarizing filter methods, a transmittance of the 3D image is low because of the patterned retarder film and the switching liquid crystal layer, each of which is disposed on the display panel to serve as a polarizing filter.
In the LC shutter glasses method, a left eye image and a right eye image are alternately displayed on the display panel every one frame, and a left eye shutter and a right eye shutter of LC shutter glasses are opened and closed in synchronization with display timing of the display panel, thereby implementing the 3D image. The LC shutter glasses open only the left eye shutter during nth frame periods, in which the left eye image is displayed, and open only the right eye shutter during (n+1)th frame periods, in which the right eye image is displayed, where n is a natural number, thereby making binocular disparity in a time division manner.
The stereoscopic image display generally uses a liquid crystal display (LCD) as a display element implementing an image. Response characteristic of the hold type display element, the LCD is slightly delayed depending on data entry. An image trailing phenomenon is generated because of the delay of the response characteristic of liquid crystals at a time when the left eye image is converted into the right eye image or at a time when the right eye image is converted into the left eye image. Hence, 3D crosstalk of ghost form appears.
An over driving control (ODC) modulation method is known to improve the response characteristic of the liquid crystals. The ODC modulation method compares previous frame data with current frame data, decides changes of data based on the comparison result, and modulates input data to a compensation value corresponding to the decision result. When a gray level of the current frame data is greater than a gray level of the previous frame data, the ODC modulation method modulates the current frame data to a value greater than an input gray level. On the contrary, when the gray level of the current frame data is less than the gray level of the previous frame data, the ODC modulation method modulates the current frame data to a value less than the input gray level. As a result, the response characteristic of the liquid crystals is improved.
However, in the ODC modulation method, when the current frame data of the same gray level is represented, a luminance deviation is generated depending on what the gray level of the previous frame data is. Thus, when the existing ODC modulation method is applied to the stereoscopic image display, it is difficult to reduce the 3D crosstalk because of the luminance deviation.
A technology has been recently proposed to remove the problem of the luminance deviation while applying the ODC modulation method to the stereoscopic image display and to reduce the 3D crosstalk. However, the technology was designed based on a national television standards committee (NTSC) format having an input frame frequency of 60 Hz. Therefore, when the technology is applied to a phase alternate line (PAL) format having an input frame frequency of 50 Hz, the problems illustrated in FIG. 1 may be generated.
In other words, as shown in FIG. 1, when the crosstalk reduction technology designed based on the NTSC format is equally applied to the stereoscopic image display using the PAL format irrespective of the input frame frequency, a liquid crystal response is achieved within a desired time to reach a target luminance of the current frame data from a luminance of the previous frame data at about 240 Hz (based on the NTSC format). On the other hand, because the time it takes to reach the target luminance of the current frame data is delayed from the desired time by a predetermined value T due to the over shoot at about 200 Hz (based on the PAL format), the 3D crosstalk is generated.
A profile of the liquid crystals varies depending on the input frame frequency. Thus, an additional complement capable of solving the problems of the crosstalk reduction technology in consideration of the input frame frequency is required.